Solar Shed

Chronicles of my efforts to install a solar powered air conditioner into our shed.

Current Goal: 4 hours runtime

Current Ability: 45 minutes runtime (nonstop compressor)

Current configuration:

(5) 100W Mono panels

(1) 20A Solar Charge Controller – MPPT (3 Panels)

(1) 20A Solar Charge Controller – PWM (2 Panels)

(1) 20A Solar Charge Controller – PWM (unused)

(1) 40A Triple CB

(1) 250A Termination Block

(1) 1500W Inverter – Pure Sine

(1) 150A ANL Fuse

(2) 12V Deep Cycle Marine Battery

(1) 410W Window AC unit

Test Conditions:

Batteries fully charged

1145AM – Winter

5 panels providing approx 300w

Test Result:

1145AM – SYSTEM OFF – 14V – 0 watts

1145AM – SYSTEM START – 13.8V – 60 watts load

1147AM – COMPRESSOR START – 12.9V -350 watts load (with 1300w short peak)

1201PM – 12.4v – 400 watts load

1210PM – 12.2V – 390 watts load

1215PM- 12.1V -TEST ENDED

1217PM – 12.8V

With the current configuration, I feel I can safely run the Air Conditioner for an hour without damaging the batteries but I know I can still do better.

Current Activity:

Just purchased a 50Ah LiFePO4 battery, DC-to-DC charge controller, and (2) more 100W mono panels

The lithium battery isnt as big as I’d like, but I can parallel more of the same kind later

This DC-to-DC charge controller should allow me to start using lithium batteries without having to toss out my existing lead acid batteries, which I think may work for a few more years just fine.

I will have multiple sources of power (when all are above 13 volts):

–> 400watts into the solar input on charge controller (had to buy 30A capable cables to parallel 4 panels with MC4)

–> DC-to-DC charge controller is really designed for vehicle living, so the ‘Alternator’ input will be my existing batteries plus 300watts from my old MPPT charge controller

<– The charge controller will only allow 25A from each simultaneously for a total of 50A going into the lithium which is its maximum

The DC-to-DC charge controller will charge both battery sets as needed automatically

Eager to see what kind of performance I will get with the lithium having the existing lead-acid batteries to extend it, plus what should now be more than enough solar to keep it flying through the heat of the day

Here is a rough sketch of how things will look with all the new stuff, front and back…

Future Plans:

(1) 150F Super Capacitor– This should help with voltage drop when compressor kicks in (from what I understand that is rough on the battery). Supercaps are known to greatly improve battery life and last a very long time, but supercaps are a bit cost prohibitive. It would seem to get the size needed to use my inverter with a constant load of 1200 watts I’d need 150F for my situation (I believe).

(1) 600W Grid-tie plugin inverter – Eventually I will produce more solar than I am consuming, so might as well throw that at our electric bill. From what I understand these are super easy, you just plug them into the wall to spin your meter backwards.

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